It is known in the art to utilize a perforated surface to assist in guiding sheets along the delivery path in a printing press. A device of this general type is disclosed in M.A.N.-Roland brochure No. 43 at page 25, a copy of which is submitted herewith. German patent specification No. 1,474,214 also discloses a device for steadying flat material being guided at a constant distance from a guide surface by means of air discharged from blowing chests which extend transversely of the direction of conveyance of the material. The walls near the plane of conveyance of the material serve as guide surfaces and are formed with blowing apertures, the air being directed towards the material in streams directed in opposite pairs to one another, the air then discharging through discharge apertures in the guide surface. Unfortunately, this system of supplying and removing the flow medium is responsible for considerable additional air eddying between the flat material and the guide surface and, therefore, for considerable additional movements of the material in this zone, more particularly at the end of a printed sheet, so that the same does not receive the necessary steady guidance.
German patent specification No. 2,724,856 discloses another solution. In sheet-fed rotary presses for selective first printing and perfecting, stationary deflectors for the sheet are provided on the sheet transfer cylinders which extend over the whole width thereof and are so arranged that an air cushion forms automatically at any speed of the press. However, in practice, these deflectors cannot totally prevent the sheet from fluttering or knocking. In this respect and according to U.S. Pat. No. 2,933,039, a negative pressure can be produced, and sheet flutter thus decreased, in perfecting presses by establishing a particular association between the sheet-conveying means and deflectors below the conveyed sheet. Similarly, according to German utility model No. 7,128,485 suction chambers can be disposed in parts at critical places of the sheet-conveying path in order to maintain the sheet in engagement with the guide surfaces, for instance, at reversal stations.